This is an excellent question, and offers an explanation why the “day” is longer than the “night” on the spring and fall equinox, when day and night are supposed to be identical.
It’s all because of the way we calculate sunrise and sunset.
If you could put a dot in the center of the Sun’s disk, then on the spring and fall equinox that dot should be exactly on the horizon 12 hours apart. However, that’s not how we determine sunrise or sunset.
Sunrise is the moment the very first sliver of the Sun’s disk appears on the horizon, when most of the Sun is still below the horizon, and sunset is the last moment a sliver of the Sun’s disk disappears below the horizon. Furthermore, due to refraction in the atmosphere, we see the Sun when it’s a little below the horizon, as the image below shows.
For those two reasons, on the equinox, when daylight and night are supposed to be exactly the same, the day is a little longer.
So sunrise is the first glimpse of the Sun as it peaks over the easterly horizon and sunset is the last glimpse of the Sun as it disappears below the westerly horizon.